Browsing by Author "Sheu, CR"

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Analysis of dielectric breakdown patterns in parallel-plate capacitors
(2000-06-01)
Sheu, CR
;
Cheng, CY
;
Wang, PS
;
Lee, CY
;
Pan, RP
The parallel-plate capacitor cells are used as model systems for studying the dielectric breakdown (DB) patterns. Air, a liquid crystal and several kinds of oils are used as the dielectric material sandwiched between the plates. We study the types of patterns formed with different materials, voltages and cell thickness. The fractal dimensions and the conditions for getting each type of DB pattern are obtained for the first time. In addition, the fractal dimensions of patterns simulated by using the active walker model (AWM) are also analyzed and compared with the experimental DB patterns.
Dielectric breakdown patterns and active walker model
(1999-02-01)
Sheu, CR
;
Cheng, CY
;
Pan, RP
;
電子物理學系
;
Department of Electrophysics
Simulations based on the active walker model an used successfully to reconstruct the dielectric breakdown patterns observed in a cell with parallel-plate electrodes. Different types of patterns can be obtained with suitable parameters. These parameters correspond to the electrical and environmental conditions during the breakdown.
Electronically tunable single and multiple wavelength broad-area semiconductor laser by using a liquid crystal pixel mirror
(2000)
Pan, RP
;
Lu, WL
;
Sheu, CR
;
Pan, CL
;
電子物理學系
Joint symbol, frame, and carrier synchronization for Eureka 147 DAB system
(1997)
Sheu, CR
;
Huang, YL
;
Huang, CC
;
交大名義發表
;
電信工程研究所
We present a joint symbol, frame, and carrier synchronization method for an OFDM signal in this paper. Symbol timing is determined first by detecting an abrupt phase change in the autocorrelation of the last quarter (e.g. Eureka 147 DAB) useful symbol and its cyclic extension in the guard interval. Frequency offset of fractional carrier spacing can be estimated from the phase angle of this autocorrelation. Coarse frame synchronization or null symbol detection can also be achieved through this information. Frequency offset of integral carrier spacing and finer frame synchronizations are determined by convolution of a received phase reference symbol and several locally generated but frequency shifted phase reference symbols. Our simulation results show that this symbol timing estimation method is less sensitive to multipath fading and the frequency offset estimation is more accurate in mobile radio channels. We also show that the algorithm is robust in both AWGN and two-path fading channels for SNR down to about 8 dB.
Joint synchronization in eureka 147 DAB system based on abrupt phase change detection
(1999-10-01)
Huang, YL
;
Sheu, CR
;
Huang, CC
;
交大名義發表
;
電信工程研究所
We present a joint symbol, frame, and carrier synchronization method for the Eureka 147 DAB signal in this paper. Symbol timing is determined first by detecting an abrupt change in the phase angle of the complex product between the last quarter of a useful symbol and its cyclic extension in the guard interval. The detection of this abrupt change is based on the maximal likelihood (ML) principle. Frequency offset of fractional carrier spacing is estimated from the phase angle of the autocorrelation after symbol timing is estimated. Coarse frame synchronization and null symbol detection can also be achieved through this correlation information Frequency offset of integral carrier spacing is determined from the convolution outputs between a received phase reference symbol and several locally generated but frequency-shifted phase reference symbols. We found the length of a yard interval is the most important parameter for the synchronization algorithm to work. Simulation results show that the performance of this synchronization method approaches to the ideal synchronization case in both an additive white Gaussian noise (AWGN) channel and a two-path Rayleigh fading channel.
Multimode optical demultiplexer for DWDM with liquid crystal enabled functionalities
(2004-10-01)
Huang, MJ
;
Pan, RP
;
Sheu, CR
;
Lan, YP
;
Lai, YF
We have developed a liquid-crystal-based multimode optical demultiplexer (DEMUX) with additional functionalities such as switching and power equalization. Demultiplexing 16-channel 100-GHz-spaced signals into a 62.5-mum multimode-fiber array is demonstrated. The central wavelength of each channel is designed according to the International Telecommunication Union grid. Adjacent channel crosstalk is less than -30 dB. The average 1- and 3-dB passbands of the DEMUX are 12.5 and 22.5 GHz, respectively. A maximum extinction ratio of 16.2 dB is achieved. Different channels can be switched with rise and fall times of similar to10 and similar to70 ms, respectively. The outputs of the channels are equalized to -65 dBm. The variation between different channels reduced from similar to10 dB to less than 0.5 dB.
Nonlinear waves induced by molecular flow in liquid crystals
(1995)
Sheu, CR
;
Pan, RP
;
交大名義發表
;
電子物理學系
;
National Chiao Tung University
Two kinds of thermotropic liquid crystals (5CB and MBBA) are used to study the director nonlinear waves induced by flow in a homeotropic nematic cell. The flow is induced by an exciter, a piece of moving mylar film at one end of the cell. Wave velocities for various exciter velocities and temperatures are measured. A ''phase'' diagram with our experimental results is constructed and compared with theoretical prediction of reentrant solitons. Waves generated in a first nematic region are observed to be able to penetrate an isotropic region and reappear in a second nematic region.
Tunable semiconductor laser with liquid crystal pixel mirror in grating-loaded external cavity
(1999-08-19)
Pan, CL
;
Tsai, SH
;
Pan, RP
;
Sheu, CR
;
Wang, SC
The wavelength of a commercial red pointer laser diode has been tuned over 4nm digitally in 0.2nm steps with a folded telescopic gating loaded external cavity incorporating a liquid crystal pixel mirror. The sidemode-suppression ratio of the laser was better than 20dB throughout this range.
Wavelength tunable semiconductor laser with a liquid crystal pixel mirror
(2002)
Pan, RP
;
Tung, HC
;
Sheu, CR
;
Pan, CL
;
Huang, MJ
Tunable semiconductor lasers are compact, versatile sources used extensively in dense-wavelength-division-multiplexing (DWDM) optical communication systems, precision metrology, environmental monitoring, and laser spectroscopy. We have developed a twisted nematic liquid crystal device, the liquid crystal pixel mirror (LCPM), successfully as electronically tunable spectral filters for wavelength selection in external cavity semiconductor lasers. In this talk, we report recent advances in this class of electronically tunable single- and multiple-wavelength semiconductor lasers at 650 and 830 nm. Preliminary results of operating the laser at 1.5 microns will also be shown. The laser output can be locked to the ITU grid at 100 GHz intervals. Output power of the laser is as high as several hundred milliwatts, with a tuning range of several tens of nanometers. The laser can be operated either in the continuous-wave (CW) or mode-locked configuration. The linewidth of the laser in the free-running CW mode is about 30 MHz. Fine-tuning of the cw output wavelength can be achieved by changing the driving voltage to the desired pixels of the LCPM. In the mode-locked configuration, the laser design allows intra-cavity dispersion compensation and pulse compression.